According to the author, what is the main reason for the decrease in trillium in the forest? What evidence does
she give to support her claim?

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .

Idon't see the pic?

Idont know. if you want an answer you need to give us some context dude.